Purpose: The purpose of this study was to compare morphine with ketamine to morphine alone in a double-blind investigation of postsurgical pain control.
Methods: Forty-two ASA 1 and 2 patients undergoing elective microdiscectomy were administered either 1 mg.ml-1 of morphine (n = 20) or 1 mg.ml-1 of both morphine and ketamine (n = 22) via iv patient controlled analgesia (IVPCA). Pain relief and side effects were assessed at 24 hr after surgery.
Results: The mean (SD) visual analogue scale (VAS) pain rating of 2.3 (1.67) for patients receiving morphine with ketamine was lower (P < 0.001) than the VAS scores of patients receiving only morphine 4.5 (1.54). Patients receiving morphine and ketamine also had less difficulty with side effects, reporting less nausea (P < 0.05), pruritus (P < 0.001), and urinary retention (P < 0.05). Although dysphoria is reported to be a common side effect of ketamine, complaints of dysphoria were rare in both groups, with only one subject (5%) in the morphine with ketamine group and three (15%) subjects receiving morphine alone reporting this side effect.
Conclusion: IVPCA ketamine in combination with morphine provides superior postsurgical pain relief at lower dosage and with fewer side effects than morphine alone.